NUCLEATION FIELDS IN AN EXCHANGE SPRING HARD MAGNET

A detailed study of magnetization processes has been carried out on a new type of hard magnetic material. The material Nd3.8Fe73.3V3.9B18.0S i1.0 is unique among hard magnets due to the exchange coupling of two ferromagnetic materials, one of which is soft and the other hard. The combination of the two materials gives a composite material, with a hi gh magnetic saturation and coercivity. The irreversible components of magnetization for the material were examined using the demagnetizing r emanence curve (DCD) and the isothermal remanence curve (IRM) for the magnetizing case. The nature of the interactions in the material were also studied using the delta M plot obtained via the DCD and IRM reman ence curves. The reversible components were obtained from the M-H loop data, M(rev)BAR = M(tot)BAR - M(irr)BAR. Measurements of magnetic tim e dependence have also been carried out to provide fluctuation field d ata, H(f), from which activation volumes of reversal, v, for various f ields have been obtained. The mean activation field H(a)BAR, obtained by extrapolating the linear portion of the fluctuation field data to z ero, is found to be the same as the mean nucleation field H(n)BAR obta ined from the reversible components, M(rev) of the demagnetizing reman ence curve. Assuming spherical volumes of reversal, the dimensions of the soft and hard phases, obtained from the mean volume of activation, v(H(n))BAR are close to the critical dimensions of the soft and hard phases.